Origin of Coronal Extreme Ultraviolet Shockwaves without a Coronal Mass Ejection Event

TL;DR

The paper investigates whether flare-accelerated particles can generate coronal EUV shock waves in the absence of CMEs by contrasting CME-associated Large-scale Coronal Propagating Fronts (LCPFs) with standalone coronal waves and sunquake energetics. Using catalogs of sunquakes, LCPFs, and CMEs, it analyzes CME-associated versus CME-less events through visual CME tagging and GOES soft X-ray flare diagnostics, deriving temperatures and emission measures from flux ratios. The results show CME-associated coronal waves are faster and linked to higher emission measures and hotter flare temperatures, while CME-less waves are slower and energetically weaker, indicating distinct generation mechanisms. Comparisons with sunquakes suggest CME-less coronal shocks are not solely sunquake-driven, implying a broader, multi-mechanism picture of how flare energy is redistributed in the solar atmosphere. The work highlights the need for extended, multi-wavelength observations and data beyond 2013 to refine models of sunquakes, EUV waves, and coronal shock generation, potentially unifying coronal seismology with helioseismology.

Abstract

A leading theory of sunquake generation involves flare-accelerated particles depositing energy into the photosphere. Simulations of sunquake excitation suggest co-excitation with wavefronts propagating in the corona and chromosphere, similar to Moreton-Ramsey waves, and large-scale coronal propagating fronts (LCPFs). To investigate observational evidence for the particle-driven mechanism in LCPFs, we compare populations of events associated with and without coronal mass ejections (CMEs). CMEs are known to generate similar EUV shock waves. We employ a visual inspection of flare events that generate LCPFs using Atmospheric Imaging Assembly (AIA) and Large Angle and Spectrometric Coronagraph (LASCO) coronagraph images to find that coronal waves associated with CMEs propagate noticeably faster. Then we examine GOES soft X-ray (SXR) data of standalone flare events (those that generate coronal waves without CMEs), focusing on soft X-ray (SXR) characteristics related to magnetic energy release rate. This reveals that such standalone or confined flares differ from sunquake flares: they are less impulsive and energetic than sunquake flares. However, they are more impulsive but less energetic than LCPF-associated flares with a CME. In particular, coronal waves accompanied by CMEs exhibit significantly higher volume emission measures, suggesting a different generation mechanism.

Figures (7)

• Figure 1: A histogram showing 171 EUV wave events (2010-2013) from the Nitta LCPF AIA movie catalog that were cross-referenced with the LASCO CME Catalog and observed for the presence of a CME using a combination of AIA and coronagraph data in 193 angstroms. The y-axis gives the total number of EUV events in the catalog and the x-axis highlights EUV wave speeds. The distribution in red includes EUV wave events that were not followed by a CME, the distribution in blue includes EUV wave events that were noticeably followed by a CME, and the orange distribution includes indeterminate events. The dashed lines indicate the corresponding log-normal distributions from the observed mean and standard deviation.
• Figure 2: (a) is a scatter plot of CME mass versus coronal wave speeds, and (b) is CME linear speed versus coronal wave speeds. The data on the x-axis was obtained via the LASCO CME catalog, while the y-axis are the 2010-2013 dates from Nitta et. al 2013.
• Figure 3: These four histograms compare certain flares of C1.0 or greater from 2010-2022, with the dotted line being the median for distribution. The red highlights flares that were associated with sunquakes as outlined in Sharykin2020, while those in blue are coronal wave flares (without a CME or filament eruption) recorded in Nitta2013. (a) is the impulsive phase duration, (b) is the characteristic energy release time estimated as the maximum value of $f_{1-8}/(df_{1-8}/dt)$, (c) is the maximum value of the SXR flux time derivative, and (d) is the SXR flux.
• Figure 4: Those in blue are the same as in Figure \ref{['fig:sunquakehistogram']}, and the green are all other flares that were not related to either sunquakes or coronal waves.
• Figure 5: Those in blue are the same as in Figure \ref{['fig:sunquakehistogram']}, and the purple are flares that do not have a sunquake, but are coronal waves that have an accompanying CME.